Traditional TV costs per thousand may still be climbing -- but that isn't the case for digital pre-roll video ads, in part due to increased inventory.Current pre-roll video advertising -- perhaps the biggest piece of the digital video category -- is down slightly at $8.18 CPMs from an $8.83 CPM during the first half of 2012, reports real-time video ad platform TubeMogul. The dip occurs when inflation has been bumping along at 2.5% per month. Most of that is due to heavy inventory, says the company. The number of daily pre-roll video ads available for real-time buying averaged 331 million ads available per day in October. There has been a monthly inventory growth rate of 7.3% in 2012, says TubeMogul.Digital video completion rates -- an increasingly important measure for digital advertisers -- continue to grow with certain formats. Top-level (tier one) sites have the higher competition rates for 15-second commercials. In the third quarter of this year, nearly 85% of viewers now watch an entire ad on top sites. This is up from nearly 82% for the first half of the year.Research also reveals that watching a completed video means better recall and brand association. There is a 20% rate of message association for those who watch a completed message, versus 8.3% for those who don't watch a completed video message. General awareness has improved to 6.9% from 3.5%.